Heat treatment of metals



time

Feb. 7, 1928. 1,658,682

c. L. IPSEN HEAT TREATMENT OF METALS Filed July 10. 1925 I temperacure temperature Inventor: Cori Llpsefi, by His Attovneg.

Patented Fa -1, 1928.

UNITED STATES M r 1,658,682 PATENT OFFICE.

Gm L m, (READY, NEW YORK, ASSIGNOR TO GENERAL ELIUIEIC OOH- rm, A CQRPORA'IION 0] NEW YORK.

iraa'r murmuor mars.

Application filed July 10, 1925. Serial 1T0. 42,779.

Q My invention relates to the heat treatment of metals for various purposes, such as hardening, refinement of grain, annealing, etc,

and has for its object the provision of a' method of and apparatus for heat treatment giving a high degree of .excellence and uni formity of results.

My invention has especial application in the heat treatment of metals for the purpose of hardening them. Ordinarily such heat treating procemes are dependent to a great degree on the skill of the operator in determining when the metal has been heated to the proper temperature- In out my invention, I maintain the temperature of the furnace at the deaccompanying drawing in which Fig.- 1 is a view showing in diagrammatic'form means for heat treating in accordance with my inyention, while Figs. 2 and 3 are views showi'cal temperature time curves produeed y my method.

Referring to the drawing, I have shown my invention in oneform as applied'to the heat treatment'of. steel= for hardening purposes. The articles to be heat treatedconsist of a stack of steel gears which are placed in an electric furnace 11 provided with a heating resistor 12.

The temperature of the furnace is automatically maintained at the proper quenching temperature for the gears 10, this temperature having been previously determined for the particular material of the gears by means of suitable tests. For the purpose of automatically controlling the temperature of the furnace a pyrometer 13' is provided which is introduced into the furnace chamber through a suitable aperture in the furnace wall and which is shown in the form of a thermocouple having its terminals connected to a suitable galvanometer 14. The pointer 15 of the galvanometer is in a position to swing over two spaced contacts 16 and 17 in response to the temperature of the furnace. Cooperating with the contacts 16 and 17 is a reciprocating contact 18 which,

during the operation of the furnace, is moved so back and forth, toward and away from the stationary contacts, but without touching them, by means of anelectric motor 19;

The adjustment of the contacts 16 and 17.

is such that the galvanometer pointer 15 05 takes up a position midway between them when the furnace is at the proper quenching tem rature, as shown in the drawing.

If the mace temperature rises above the quenching temperature a predetermined amount, for example two degrees 0., the pointer'15 will move to the ri ht over the contact 17 and will be squeezed tween this contact and the reciprocating contact 18 upon the next downward movement of the latter. This closes a circuit from the supply source 20 through an operating coil'21 which thereupon throws a switch arm 22 to the left out of contact with the stationary contacts 23 whereby the circuit of the coil 21 and also so an pperating coil 2 is opened. The d'eenergization of coil 24 allows the contactor switch 25 to move to open position and thereby disconnect the resistor 12 from the supply circuit 20. The switch arm 22 when 5 thrown to the left comes to rest in engagement w1th a pair of stationary contacts 26 wliilicgz are in circuit with an operating co As the temperature of the furnace nowy falls, due to deenergization' of the resistor 12, the pointer 15 moves toward the left and upon the occurrence of a predetermined minlmum temperature which may, for example, be five degrees below the desired quenching temperature, thepointer movesabove the stationary contact 16. When in this position the pointer is squeezed between the stationary contact 16 and the reciprocating conl tact 18 and a circuit thereby closed through the coil 27 whereby the switch arm 22 is thrown back to the right into engagement with the contacts 23 and the circuit of the coil 24 thus completed, the circuit, of the coil 27 being opened by the disengagement of 10;,

now rises and upon the reoccurrence of the predetermined maximum temperature, the pointer 15 is again movedover thestationary contact- 17, whereupon the control cycle is repeated as previously described. The furnace temperature is thus maintained automatically at the desired quenching temperature within predetermined minimum and maximum limits Obviously anysuitable system can. beused for automatically regulating the temperature of the furnace.

A second pyrom'eter 30, shown as a thermocouple, is introduced through a suitable aperture in-the furnace wall, and placed in. close proximity to the stack of gears 10 so' as to be responsive to the temperature of the gears rather than to the temperature of the furnace interior. As shown, the yroin eter 30 is placed inside the stack 0 gears. This pyrometer is connected to algalvanom- 'beter, notshown, which is provided with a pointer 31 forming apart of arecording in strument 32. of any suitable' formh The pointer 31 carries suitable means, such, as ink, for inscribing a line 33 on.,a strip of paper or chart-.34, which is moved beneath V it at a uniform rate. .The line 33 thustakes the form of a temperature time curve for the stack of gears. 1 v

. In heat treating materials in accordance 39 v with my invention the furnace is started and "heated while empty to the desired quenching temperature of themateriah Atthis time'the pyrometer is exposed to thetemg perature of the interior of the. furnace; and

35 the pointerl31, therefore inscribes a straight. llne 35, as indicated in Fig. 2; When the furnace temperature has reached the predef termined quenching temperature for which the automatic regulating mechanism is-set,"

I the pointer 31 is adjusted, if necessary, to"

rest'on a reference line'or mark 36 on the. chart, this reference linebeing in a directlon to represent some predetermined tenix' perature, i. e., in the direction. ofmovement i of the chart. This adjustmentof the pointer can conveniently be made by varyingthe electrical resistance in circuit with the pyv rometer 30 for example by adjusting a rheoe;

stat 32 included in its circuit. When the pointer 31 is this set on this line, the line becomes an indication of the quenching temperature for the charge. Thepointer 31 Wlll now make a zigzag line as indicated at 37 (Flg. 2) due to the small variations in temperature between the maximum and minimum limits occurring under the automatic regulator mechanism. Y After the apparatus has been thus adusted, the charge or stack of gears 10 to be treated'is placed in the furnace in the locat1 on with respect to the pyrometer 3O prevlously descrlbed. The pointer 31 now de scribes the nearly straight portion 38 (Fig. 2) of the curve indicating a rapidly falling temperature due to the fact that the pyromthe reference line at this temperature;

1600 F. As before, 'the operator has sim eter 30 is now exposed to the cold gears 10. As the temperature of the gears begins to rise the pointer 31 moves back toward the reference line 36 inscribing the portion of the curve '39, the rate of temperature rise decreasing rapidly as indicated by, the increasing curvature of this portionofthe curve. When the temperature of the chargeis near the quenching temperature, i. e., the temperature of the furnace, the curve 33 approachesfparallelism with the reference'line 36 indicating a slow increase intemperature. This period of slow temperature rise gives the charge an opportunity to become uniformly heated throughout. v 8

Throughout. the heating operation, the

furnace operator, simply watches the position of the pointer 31 with respect to the reference line 36, and when the pointer rests on the 'referenceline the operatorv removes the charge and quenches it. 1 It is not necessary for the operator to readtemperatur es or even to know the quenching temperature. He has simply to note when the pointer rests on the referenceline. The success of theprocessis therefore not dependent to any great-extent'upon the degree of skill and care exercised bythe operator.

If desired, in order toshorten the heating period and thereby increase the capacity of the furnace, the temperature 1n the furnace may be maintained somewhat higher than the desired final temperatureof the charge. When this is done the furnace and recbrding instrument32 are initially 'adjusted, as previously described, with the furnace 'impty and; automatically maintained at the desired lquen chin'g temperature. in such manner that the pointer 31 rests 'on Thereafter the automatic mechanism is set to maintain. a higher furnace temperature. This adjustment may be made in the arrangement shown by moving the two contacts 1,6 and "17 together/coward the right a predetermined amount. With the furnace maintained at this higher temperature -.the rate of heating of the charge will be more rapid as indicated by the more gfadual curvature ofthe heating-portion 40 ofthe curve shown in Fig. 2. Forexample, with a desired quenching temperature of 1500 F., the furnace control mechanism may be set to maintain a temperature of ply to watch the pointer 31 of the recordinginstrument' and. uench the charge when the pointer rests on t e reference line 36.

While -I have described my invention as embodied in. concrete form and as operat-' ing in a specific manner in accordance with" the provisions of thepatent statutes, 'it should be understood that I do not-limit my invention thereto, since various modifications thereof will suggest themselves to those J skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States,

1. The method of hardening steel which consists in heating a furnace while empty to the proper quenching temperature of the steel, setting a charge temperature indicator on a definite reference mark at this temperature, placing a charge of said steel in said furnace whereupon the charge temperature indicator shows the temperature of said charge, maintaining the temperature of said furnace at least as high as said quenching temperature, noting the approach of said charge temperature indicator to said reference mark as the charge is heated, and then quenching the charge when said indicator is approximately on said reference mark.

2. In the heat treatment of metal, the method of heating the metal in a furnace provided with a temperature indicator close- 1y associated with the charge so as to indicate the ten'lperature of the charge, which consists in heating the furnace Without a charge to the desired temperature for the metal, whereby said charge temperature indicator is subjected to said temperature, setting the charge temperature indicator on a definite fixed reference mark while maintaining the furnace at said desired temperature,

inserting a cold charge in said furnace whereupon the charge temperature indicator shows the temperature of the charge, maintaining the furnace temperature at approximately said desired ten'iperature of the charge as the charge is heated, noting the approach of the charge temperature indicator to the reference mark ast-he temperature of the charge approaches the temperature of the furnace, and then removing the charge when the indicator is approximately on said reference mark.

In witness whereof, I have hereunto set my hand this 9th day of July 1925.

- CARL L. IPSEN. 

